An association exists between dietary animal protein and calcium stone formation. High protein leads to increased endogenous acid production and subsequent proton induced bone dissolution. We propose that dietary acid load is one of the factors controlling the calcium excretion rate in patients with calcium kidney stone disease and idiopathic hypercalciuria. The effects of changing dietary acid load on urinary calcium excretion and calcium balance in patients with idiopathic hypercalciuria will be studied.